Physicists like Lord Kelvin did not, however, care about the opinion of either literalists or biologists, so their arguments had little impact.But this age for the sun was troublesome also in astronomy; the sun was only one star among many, and if it was assumed, reasonably enough, that all stars worked the same way, contradictions followed.Stars of all sizes should start out cool, get hotter and denser, and then finally cool off again and end up as cold compact objects.Larger, more massive stars should generally be more luminous than smaller ones, but there is no reason to expect a relation with temperature.This stands in stark contradiction with the discovery by Hertzsprung and Russell (Hertzsprung 1905; Russell 1914) that the vast majority of stars do give such a pattern, when plotted in what is now known as a Hertzsprung-Russell diagram (e.g. Eddington (1924) developed these ideas further, and showed that the only reasonable conclusion is that stars start out contracting (and shining from gravitational energy), but that they then reach equilibrium along what is now known as the "main sequence".Gravitational energy cannot account for that equilibrium; a new energy source is needed.Finally, the creationist arguments concerning solar neutrinos, and other solar anomalies, real and fictional, will be treated.
This anomaly persisted until quite recently, and is known as the "solar neutrino problem".
Another argument comes from variable stars (Eddington 1920).
Many stars oscillate regularly, but an ongoing contraction would measurably change the oscillation frequency, in a matter of decades.
William Thomson (better known as Lord Kelvin) elaborated and promulgated this theory during the last decades of the 19 century.
It was clear, however, that this energy source, while ample by human standards, couldn't last forever.